The present invention relates to intravascular, gastrointestinal, or urological guide wires, and methods of manufacture therefor. In particular, the present invention relates to multi-layered intravascular guide wires, and methods of manufacture therefor.
Guide wires are used in various procedures in both the coronary regions and the peripheral regions of the body. Various sizes and lengths of guide wires are made to be suitable for various uses and locations in the body. For example, guide wires of very small diameters, on the order of 0.010 to 0.018 inches, may be suitable for use in narrow coronary vessels. Such guide wires may have an extremely floppy distal tip which may be bent or preformed by the physician to facilitate placement of the guide wire at the desired location. Other guide wires have a larger diameter, for example 0.035 inches, and preformed tip. These larger diameter guide wires may be especially useful in peripheral or gastrointestinal regions of the body. Larger diameter guide wires may be provided with very flexible tips or with relatively rigid tips depending upon the particular needs of the patient and the preferences of the physician. Guide wires come in a range of sizes in addition to those discussed above.
Some of the preferred characteristics in a guide wire include support, the ability to provide a track for a balloon or other device to advance over, and good torsional transmittance. A discussion of these and other preferred characteristics of guide wires can be found in Endovascular Surgery, by Moore, W. S. and Ahn, S. S.; p. 157, W. B. Saunders Co. (1989). Other characteristics that are often desirable include flexibility, strength, radiopacity, color, lubricity, etc.
In many cases, providing a desired combination of guide wire characteristics can be a significant engineering challenge. In some cases, the approach used to enhance one guide wire characteristic may adversely affect another. For example, suppose a guide wire includes a plastic jacket around the distal tip of a guide wire core for support. The radiopacity of the guide wire tip may be enhanced by loading the plastic jacket with a high concentration of a radiopaque agent. However, by providing a high concentration of a radiopaque agent, the tensile strength of the plastic jacket is typically reduced. Thus, the strength of the distal tip of the guide wire is reduced, and the flexibility may be unduly reduced. This illustrates the often difficult balance between competing characteristics of a typical guide wire design.
The present invention provides a multi-layered guide wire that uses separate layers to achieve desired guide wire characteristics. Each of the layers may enhance one or more desired guide wire characteristics, with the combination of layers providing the desired combination of guide wire characteristics. Each of the layers may be provided over the entire guide wire, or only over selected portions of the guide wire. Further, selected layers may be co-extruded over the guide wire, which may reduce the manufacturing costs associated with the multi-layer guide wire design.
In one illustrative embodiment of the present invention, a guide wire is provided that includes an elongated core with an outer axial surface. At least two outer jacket layers are co-extruded over at least a portion of the outer axial surface of the elongated core, and preferably over only the distal portion thereof. Each of the at least two outer jacket layers preferably have at least one physical property that differs from another one of the outer jacket layers. Illustrative physical properties include flexibility, radiopacity, strength, color, bonding characteristics, lubricity, etc.
In another illustrative embodiment of the present invention, a first and a second outer jacket layer are co-extruded over the distal end of the elongated core. The first outer jacket layer, which is disposed closest to the elongated core, may include a plastic that is loaded with a relatively high concentration of a radiopaque agent, such as tungsten, tantalum, platinum, gold, etc. This enhances the radiographic signature of the distal end of the guide wire. As indicated above, however, loading the first outer plastic jacket layer with a relatively high concentration of a radiopaque agent typically reduces the tensile strength thereof. To compensate for the reduced strength, the second outer jacket layer, which preferably has little or no radiopaque agent therein, is provided over the first outer plastic jacket. The combination of the first and second outer jacket layers provides a guide wire that has a highly radiopaque distal tip, and yet retains the desired strength characteristic.
In another illustrative embodiment, a first and a second outer jacket layer are co-extruded over selected portions of the elongated core. The term xe2x80x9cselected portionsxe2x80x9d includes the entire elongated core, various sections of the elongated core, the distal tip of the core, etc. In this embodiment, the first outer jacket layer, which is disposed between the elongated core and the second outer jacket layer, is formed from a bonding material that is particularly suited for forming a bond between the second outer jacket layer and the elongated core. This provides an efficient method for bonding a plastic jacket to an elongated core, and in particular a metallic elongated core, without having to apply an adhesive or the like to the elongated core by conventional methods such as dipping or spraying. It has been found that this may reduce the cost of producing a guide wire that has one or more plastic jacket layers thereon.
It is contemplated that the bonding layer may be co-extruded with any number of layers. For example, a guide wire may be formed by co-extruding a bonding layer, an inner plastic jacket and an outer plastic jacket over at least a portion of an elongated core. The inner plastic jacket may, for example, have a first concentration of a radiopaque agent, and the outer plastic jacket may have a second concentration of a radiopaque agent. The bonding layer preferably forms a bond between the elongated core and the inner plastic jacket. A lubricious layer may be co-extruded along with the bonding layer, the inner plastic jacket and the outer plastic jacket to provide a lubricous outer surface thereto.
Finally, and in another illustrative embodiment of the present invention, a number of outer jacket layers are co-extruded over a mandrel or the like to produce a multi-layer tip assembly having a lumen. In one embodiment, the distal end of a guide wire is positioned in the lumen and the tip assembly is heated. By selecting the appropriate materials, the multi-layer tip assembly may shrink as a result of the heating process, securing the tip to the distal end of the guide wire. In another embodiment, a bonding adhesive may be used, wherein the bonding adhesive may be pressure activated or heat activated. Thus, the tip assembly may be secured to the distal tip of the guide wire by simply applying pressure or heat as appropriate.